ELECTRICAL PHENOMENA

Evening Star, Issue 19697, 26 October 1927, Page 2

ELECTRICAL PHENOMENA

SOLAR AHD TERRESTRIAL RELATIONS At a meeting of tli'o astronomical branch of the Otago Institute, held last night, a lecture was given by l)r (J. M. Fockcu on ‘ Relations Uetween fciolar and Terrestrial Electrical Phenomena.’ Tho 1 lecture was illustrated by appropriate slides and experiments, mostly relating to solar phenomena—e.g., sunspots, eclipses, prominences, corona, etc. — and to the magnetic effect on light. Certain phenomena observed on the earth cannot reasonably bo attributed to causes in the earth itself, and many of. the most important ot these arc found to be related in a fairly definite, hut not completely understood, manner with the sun and radiations emitted from it, said the lecturer, who showed how astrophysicists had submitted tho sun to a detailed examination and tho deductions that had been drawn. The key instrument by which they have unlocked many solar secrets is the spectroscope, and in recent years this has been considerably modified by Halo ami by Deslandrcs, giving rise to tho spectrnhoiiograph and the spectrohclioscopo. Tho former allowed them to determine tho distribution of a particular element over tho sun’s surface; in fact, they could permanently record this by photographing tho sun iu tho light corresponding to one of the wave lengths peculiar to tho element. The spcctrohelioscopc had very recently been invented bv Hale and used by him to actually watch the changes in the distribution of a. particular element in the sun’s atmosphere, and ho had oßen observed by U. masses of glowing hydrogen gas (flocculi) being sucked into the tremendous vortex of gases which scientists now believed constituted a sun spot. Free electrons, of which there were swarms present in the incandescent vapors round the sun, joined in this vortex movement, and so constituted a circular electric current round a sun spot, and this produced a magnetic hold perpendicular to the solar surface along the axis ot the spot. This magnetic field, and also the general magnetic held found to ho associ.ued with the sun, had been detected and measured by moans of tho Zeeman effect on the spectral lines produced by tho glowing vapors round the sun. Zeeman proved by laboratory experiments that a magnetic field splits the spectral line into components, and tho amount of separation of these components gave a measure of the magnetic Held.

Many of the amazing peculiarities of the sun spots were mentioned —their bipolar nature, the limitation to certain latitudes or the sun, the opposite polarities in the two hemispheres, the well-marked periodic variation in frequency in a cycle of about eleven years, the reversal of all polarities at each sun snot minimum—and it was shown lioav the modern vortex theory accounted for many of them. From .similar periodic changes shown to take place in the number and latitudes ol solar prominences and in the shape of the corona it has been deduced that this eloveu-ycar period is really a general cycle of solar activity. The very interesting connections between this cycle of general solar activity and certain terrestrial phenomena were next discussed. The correlation coefficient method of obtaining a relation between these variables was stated. It was shown that Dr Walker, an eminent meteorologist in India, had been able to definitely correlate the sunspot activity and »lic Indian monsoon rainfall, and so had been able to considerably improve his predictions ol that rainfall, lint this method, as it was not yet well understood, had proved ot little general importance in weather forecasting. It was demonstrated by means ol graphs that the average diurnal variations in the magnetic elements also follow an eleven-year period, which is, in fact, almost coincident with that of the solar activity. Many lines of evidence led to the conclusion that the sun ionised the upper layers of the earth’s atmosphere by two independent agencies—firstly, _ ultraviolet radiation, which fell mainly on the sunlit hemisphere of the earth, and, secondly, an electrical corpuscular radiation, which emanated from particular areas on the sun, and because of its charge was concentrated in the regions of the earth’s magnetic poles, The ultra-violet radiation was absorbed in the upper atmosphere principally by ozone, and it produced an upper ionised layer, which was of great importance in explaining the transmission of wire less waves round the earth and the normal diurnal magnetic variations. The corpuscular radiation was the cause of the magnetic storms and accompanying auroral displays on the earth, but there were still many difficulties in explaining in this way the remarkable characteristics of these phenomena. The most remarkable was the well-cstablisned recurrence tendency shown by magnetic storms, which tend'd to reappear in a less intense form at; intervals of 27 days; but this could be explained if they pictured the corpuscular radiation as a jot of charged particles (ions) shot out by light pressure from a particular area on the sun’s surface. If this area remained fixed on the sun’s surface and the jet in a definite direction, tho jet of ions would engulf the earth suddenly each time the sun rotated, and it was well known that this rotation took ebout twenty-seven days, as seen from the earth. Visual evidence of tho luminosity produced in tho upper atmosphere by these ionic jets was provided by the auroral displays accompanying magnetic storms. The spectrum of the aurora lent great weight to the theory that it was produced by an electric discharge in our atmosphere, for it showed principally green bands duo to nitrogen, and lines due to argon, neon, and xenon had also been detected in it. Within tho last few months Dr M'Lcnnan, working at. Toronto University, had definitely proved that the prominent and hitherto nnascribed yellow-green lino found in the auroral spectrum and in tho spectrum of tho night sky was produced by oxygen, greatly enhanced by the presence of the rare gases. The influence of the upper ionised layer on wireless transmission was lastly considered.

Dr Jack, Ur Lawson, and tho lecturer took part in a brief discussion on the value of correlation coefficients. The thanks of the astronomical branch and the audience were tendered to Ur Focken by the president (Dr C. M. Hector).